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Configure a Session Border Controller for multiple tenants

  • Article
  • Applies to:
    Microsoft Teams

Direct Routing supports configuring one Session Border Controller (SBC) to serve multiple tenants.

Note

This scenario is designed for Microsoft partners and/or PSTN carriers, referred to as carriers later in this document. A carrier sells telephony services delivered to Microsoft Teams to their customers.

A carrier:

  • Deploys and manages an SBC in their datacenter (customers don't need to implement an SBC, and they receive telephony services from the carrier in the Teams client).
  • Interconnects the SBC to multiple tenants.
  • Provides Public Switched Telephone Network (PSTN) services to customers.
  • Manages call quality end to end.
  • Charges separately for PSTN services.

Microsoft doesn't manage carriers. Microsoft offers Phone System—a Private Branch Exchange (PBX)—and a Teams client. Microsoft also certifies phones, and certifies SBCs that can be used with Phone System. Before choosing a carrier, ensure that your choice has a certified SBC and can manage voice quality end to end.

The following are the technical implementation steps to configure the scenario.

Carrier only:

  1. Deploy the SBC and configure it for the hosting scenario according to the instructions from the certified SBC vendors.
  2. Register a base domain name in the carrier tenant and request a wildcard certificate.
  3. Register a subdomain for every customer, which is part of the base domain.

Carrier with a Customer Global Administrator:

  1. Add the subdomain name to the customer tenant.
  2. Activate the subdomain name.
  3. Configure the trunk from the carrier to the customer tenant and provision users.

Make sure you understand DNS basics and how the domain name is managed in Microsoft 365. See Get help with Microsoft 365 domains before proceeding further.

Deploy and configure the SBC

For detailed steps on how to deploy and configure SBCs for an SBC hosting scenario, see the SBC vendor's documentation.

Note

Make sure you know how to configure the "Contact" header. The Contact header is used to find the customer tenant on the incoming invite message.

Register a base domain and subdomains

For the hosting scenario, you need to create:

  • One base domain name owned by the carrier.
  • A subdomain that is part of the base domain name in every customer tenant.

In the following example:

  • Adatum is a carrier that serves several customers by providing Internet and telephony services.
  • Woodgrove Bank, Contoso, and Adventure Works are three customers that have Microsoft 365 domains but receive the telephony services from Adatum.

Subdomains MUST match the FQDN name of the trunk that will be configured for the customer and the FQDN in the Contact header when sending the Invite to Microsoft 365.

When a call arrives at the Microsoft 365 Direct Routing interface, the interface uses the Contact header to find the tenant where the user should be looked up. Direct Routing doesn't use phone number lookup on the Invite, as some customers might have non-DID numbers that can overlap in several tenants. Therefore, the FQDN name in the Contact header is required to identify the exact tenant to look up the user by the phone number.

For more information about creating domain names in Microsoft 365 organizations, see Get help with Microsoft 365 domains.

The following diagram summarizes the requirements to base domain, subdomains, and Contact header.

Diagram showing requirements to domains and Contact header.

The SBC requires a certificate to authenticate the connections. For the SBC hosting scenario, the carrier needs to request a certificate with CN and/or SAN *.base_domain (for example, *.customers.adatum.biz). This certificate can be used to authenticate connections to multiple tenants served from a single SBC.

The following table is an example of one configuration.

New domain name Type Registered Certificate CN/SAN for SBC Tenant default domain in the example FQDN name that SBC must present in the Contact header when sending calls to users
customers.adatum.biz Base In carrier tenant *.customers.adatum.biz adatum.biz NA, this is a service tenant, no users
sbc1.customers.adatum.biz Subdomain In a customer tenant *.customers.adatum.biz woodgrovebank.us sbc1.customers.adatum.biz
sbc2.customers.adatum.biz Subdomain In a customer tenant *.customers.adatum.biz contoso.com sbc2.customers.adatum.biz
sbc3.customers.adatum.biz Subdomain In a customer tenant *.customers.adatum.biz adventureworks.com sbc3.customers.adatum.biz

To configure the base and subdomains, follow the steps described below. This example configures a base domain name (customers.adatum.biz) and a subdomain for one customer (sbc1.customers.adatum.biz in Woodgrove Bank tenant).

Note

Use sbcX.customers.adatum.biz to enable voice in the carrier tenant; sbcX can be any unique and valid alphanumeric hostname.

Register a base domain name in the carrier tenant

These actions are performed in the carrier tenant.

Ensure that you have appropriate rights in the carrier tenant

You can only add new domains if you signed in to the Microsoft 365 admin center as a Global Administrator.

To validate the role you have, sign in to the Microsoft 365 admin center (https://portal.office.com), go to Users > Active Users, and then verify that you have a Global Administrator role.

For more information about admin roles and how to assign a role in Microsoft 365, see About admin roles.

Add a base domain to the tenant and verify it

  1. In the Microsoft 365 admin center, go to Setup > Domains > Add domain.

  2. In the Enter a domain you own box, type the FQDN of the base domain. In the following example, the base domain is customers.adatum.biz.

  3. Click Next.

  4. In this example, the tenant already has adatum.biz as a verified domain name. The wizard will not ask for additional verification because customers.adatum.biz is a subdomain for the already registered name. However, if you add an FQDN that has not been verified before, you'll need to go through the process of verification. The process of verification is described below.

  5. Select Next, and on the Update DNS Settings page, select I'll add the DNS records myself and select Next.

  6. On the next page, clear all values (unless you want to use the domain name for Exchange, SharePoint, Teams, or Skype for Business), select Next, and then select Finish. Make sure your new domain is in the Setup complete status.

Activate the domain name

After you have registered a domain name, you need to activate it by adding at least one Teams licensed user or resource account. Acceptable accounts will be licensed with any one of the following SKU’s:

  • User Account with Office 365 E1/E3/E5 or Microsoft 365 E3/E5.
  • User Account with Office 365 A1/A3/A5 or Microsoft 365 A1/A3/A5.
  • User Account with Office 365 F3 or Microsoft 365 F1/F3.
  • User Account with Office 365 G1/G3/G5 or Microsoft 365 G3/G5.
  • User Account with Microsoft 365 Business Basic/Standard/Premium.
  • User Account with a Microsoft Teams Shared Devices license.
  • Resource Account with a Microsoft Teams Phone Resource Account license.

Additionally the account’s UPN (User Principal Name) or Skype for Business on-premises SIP address must use the same FQDN as the newly created domain.

For more information about adding users in Microsoft 365 organizations, see Get help with Microsoft 365 domains.

For example: test@customers.adatum.biz

Screenshot of the base domain activation page.

Register a subdomain name in a customer tenant

You'll need to create a unique subdomain name for every customer. In this example, we will create a subdomain sbc1.customers.adatum.biz in a tenant with the default domain name woodgrovebank.us.

All actions below are in the customer tenant.

Ensure that you have appropriate rights in the customer tenant

You can only add new domains if you signed in to the Microsoft 365 admin center as a Global Administrator.

To validate the role you have, sign in to the Microsoft 365 admin center (https://portal.office.com), go to Users > Active Users, and then verify that you have a Global Administrator role.

For more information about admin roles and how to assign a role in Microsoft 365, see About admin roles.

Add a subdomain to the customer tenant and verify it

  1. In the Microsoft 365 admin center, go to Setup > Domains > Add domain.

  2. In the Enter a domain you own box, type the FQDN of the subdomain for this tenant. In the example below, the subdomain is sbc1.customers.adatum.biz.

  3. Select Next.

  4. The FQDN has never been registered in the tenant. In the next step, you'll need to verify the domain. Select Add a TXT record instead.

  5. Select Next, and note the TXT value generated to verify the domain name.

    Screenshot of text records on the Verify domain page.

  6. Create the TXT record with the value from the previous step in the carrier's DNS hosting provider.

    For more information, see Create DNS records at any DNS hosting provider.

  7. Go to the customer's Microsoft 365 admin center and select Verify.

  8. On the next page, select I'll add the DNS records myself and select Next.

  9. On the Choose your online services page, clear all options and select Next.

  10. Select Finish on the Update DNS settings page.

  11. Ensure that the status is Setup complete.

    Screenshot of page showing status of Setup complete.

Note

The base URL and the subdomain for the individual client have to be on the same tenant to enable you to add a direct route trunk.

Activate the subdomain name

After you have registered a subdomain name, you need to activate it by adding at least one Teams licensed user or resource account. Acceptable accounts will be licensed with any one of the following SKU’s:

  • User Account with Office 365 E1/E3/E5/A3/A5 or Microsoft 365 E3/E5/A3/A5
  • User Account with Office 365 F1/F3 or Microsoft 365 F1/F3
  • User Account with Microsoft 365 Business Basic/Standard/Premium and G3/G5 plans
  • User Account with a Microsoft Teams Shared Devices license
  • Resource Account with a Microsoft Teams Phone Resource Account license

Additionally the account’s UPN (User Principal Name) or Skype for Business on-premises SIP address must use the same FQDN as the newly created subdomain.

For more information about adding users in Microsoft 365 organizations, see Get help with Microsoft 365.

For example: test@sbc1.customers.adatum.biz

Screenshot of the Activation of the subdomain page.

Create a trunk and provision users

With the initial release of Direct Routing, Microsoft required a trunk to be added to each served tenant (customer tenant) using the New-CSOnlinePSTNGateway cmdlet.

However, this method has not proved optimal for two reasons:

  • Overhead management. Offloading or draining an SBC, for example, changes some parameters, like enabling or disabling media bypass. Changing the port requires changing parameters in multiple tenants (by running Set-CSOnlinePSTNGateway), but it is in fact the same SBC.

  • Overhead processing. Gathering and monitoring trunk health data - SIP options collected from multiple logical trunks that are, in reality, the same SBC and the same physical trunk, slows down processing of the routing data.

Based on this feedback, Microsoft is bringing in a new logic to provision the trunks for the customer tenants.

Two new entities were introduced:

  • A carrier trunk registered in the carrier tenant by using the command New-CSOnlinePSTNGateway. For example:

    New-CSOnlinePSTNGateway -FQDN customers.adatum.biz -SIPSignalingport 5068 -ForwardPAI $true

  • A derived trunk that doesn't require registration. It is simply a desired host name added in from of the carrier trunk. It derives all of its configuration parameters from the carrier trunk. The association with the carrier trunk is based on the FQDN name (see details below).

Provisioning logic and example

  • Carriers need to set up and manage only a single trunk (the carrier trunk in the carrier domain) by using the Set-CSOnlinePSTNGateway command. In the example above it is adatum.biz.

  • In the customer tenant, the carrier needs to add the derived trunk FQDN to the voice routes. There is no need to run New-CSOnlinePSTNGateway for a trunk.

  • The derived trunk, as the name suggests, inherits or derives all the configuration parameters from the carrier trunk.

Examples:

  • Customers.adatum.biz – the carrier trunk which needs to be created in the carrier tenant.

  • Sbc1.customers.adatum.biz – the derived trunk in a customer tenant. You can add the name of the derived trunk in the customer tenant in the voice routes without creating it.

  • Carrier will need to set up DNS record resolving derived trunk FQDN to carrier SBC IP address.

  • Any changes made on a carrier trunk (on carrier tenant) are automatically applied to derived trunks. For example, carriers can change an SIP port on the carrier trunk, and this change applies to all derived trunks. New logic to configure the trunks simplifies the management as you don't need to go to every tenant and change the parameter on every trunk.

  • The options are sent only to the carrier trunk FQDN. The health status of the carrier trunk is applied to all derived trunks and is used for routing decisions. Find out more about Direct Routing options.

  • The carrier can drain the carrier trunk, and all derived trunks will be drained as well.

Note

Number translation rules applied on the carrier trunk don't apply to derived trunks. This is a known issue. As an alternative solution, number translation rules must be created for each customer's tenant. Some functionality can be configured only by using PowerShell; for example, adding a new voice route. You must use the New-CsOnlineVoiceRoute cmdlet. In such cases, follow the guidance presented in other sections of this documentation related to cmdlets.

Migration from the previous model to the carrier trunk

For migration from the current implementation of the carrier hosted model to the new model, the carriers will need to reconfigure the trunks for customer tenants. Remove the trunks from the customer tenants using Remove-CSOnlinePSTNGateway (leaving the trunk in the carrier tenant)-

We highly encourage migrating to the new solution as soon as possible as we will be enhancing monitoring and provisioning using the carrier and derived trunk model.

For more information about configuring sending the FQDN name of subdomains in the Contact header, see the SBC vendor instructions.

Considerations for setting up multi-tenant failover

To set up failover for a multi-tenant environment, you'll need to do the following:

  • For each tenant, add the FQDNs for two different SBCs. For example:

    customer1.sbc1.contoso.com
    customer1.sbc2.contoso.com

  • In the Online Voice Routes, specify both SBCs. If one SBC fails, the routing policy will route calls to the second SBC.

See also

Plan Direct Routing

Configure Direct Routing